A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate
The patterning device may be transmissive or reflective. In both cases, the patterning device includes a pattern, the pattern either influencing a transmission or a reflection of a part of the patterning device. The pattern may, e.g., include a patterned layer of a metal such a chrome. To prevent a transfer (i.e. a transmission or a reflection) of radiation outside a useful (e.g. patterned) part of the patterning device. A remainder of a surface of the patterning device may be covered with a material preventing transmission, resp. reflection. A manufacturing of such a layer on the patterning device is highly costly and needs to comply with high optical standards to prevent any transmission of radiation at a part of the patterning device where such transmission is not desired. Commonly, a lithographic apparatus over its lifetime makes use of a plurality of different patterning devices. To lower a cost of manufacturing of such patterning devices and/or to relax requirements thereon, a so-called reticle masking device may be provided in the lithographic apparatus. The reticle masking device masks an unused, i.e. “a blind” part of the reticle, the reticle masking device thus preventing an irradiation of the unused part of the reticle, and therefore relaxing requirements in terms of residual transmission resp. residual reflection thereof
In a so-called scanner, and possibly also in other types of lithographic apparatuses, the reticle makes a scanning movement following a scanning of the substrate. The reticle masking device is required to follow at least a part of the movements of the reticle to be able to effectively mask an unused part of the reticle. In conventional lithographic apparatus, it is common that the reticle masking device is physically smaller then the reticle itself, as the reticle masking device is positioned in an optical projection system of the lithographic apparatus at a position where the reticle masking device will be optically enlarged to scale it to a size of the reticle. In future designs of lithographic apparatuses, due to requirements of the projection system, such a scaling of the reticle masking device with respect to the reticle is to be prevented to meet a variety of design requirements of the lithographic apparatus. Therefore, a dimension of the reticle masking device is required to increase, in a practical embodiment, e.g., by a factor 4 in all three dimensions, hence significantly increasing its building volume and mass. Also, due to the larger physical dimensions of the reticle masking device, accelerations and decelerations thereof to follow a scanning movement of the reticle, will increase. Also, the higher mass in combination with the larger accelerations will require much higher forces to accelerate and decelerate the mask as well as potentially result in much higher disturbances (i.e. mechanical evaporations) in a remainder of the lithographic apparatus.